short circuit MVA rating
short circuit MVA rating
(OP)
I am trying to determine what the 3 phase and 1 phase MVA short circuit rating is for my shop. Do I need to request this information from my utiliy provider or is there another way of determining this?
Also if the utility enters a main building and that main building supplies multiple buildings under it will the short circuit rating be the same for all sub buildings or will they be different ?
Also if the utility enters a main building and that main building supplies multiple buildings under it will the short circuit rating be the same for all sub buildings or will they be different ?






RE: short circuit MVA rating
RE: short circuit MVA rating
The sub building I'm looking at has a main breaker with a rating of 400A at 600v. Would I be safe to say the short circuit current is the breaker maximum of 400A? and if so then I could just assume the short circuit MVA rating for the building would be = (sqrt 3 * 600v * 400A)/6
RE: short circuit MVA rating
For a more accurate estimate, a calculation need be performed and necessary source and circuit impedance and other related information need to be known.
The cables and transformers between the main building and the sub-building will reduce the available SC current at the sub building.
Rafiq Bulsara
http://www.srengineersct.com
RE: short circuit MVA rating
RE: short circuit MVA rating
Sqrt 3 x 600 x 400 = the VA rating of the circuit without the division by 6.
Also am curious why you decided to divide by 6?
As was stated before, you should either get the info from the utility or get some help to come up with a conservative estimate of the available fault duty.
Alan
RE: short circuit MVA rating
I got the info from the utility which was stated as
5.425 MVA sc L-L-L
3.744 MVA sc L-G
Xl/Rl 3.74
X0/R0 3.63
These are the ratings at the main. From the main it then feeds into a distribution panel and on the panel is one 400A breaker that feeds the building in question. If I did know the cable size, length, and type feeding the building from the 400A breaker how would I get a closer aproximation of this buildings fault rating?
RE: short circuit MVA rating
5.425 MVA sc
4.697 MVA sc
RE: short circuit MVA rating
Alan
RE: short circuit MVA rating
Matt:
If you asked your question correctly to the utility co, go with their answer. If in doubt, consult some professional engineer with all the info on hand.
Rafiq Bulsara
http://www.srengineersct.com
RE: short circuit MVA rating
fault current is:
5224A three phase and 4524A line to ground fault.
I have used these parameters in the modeling software I am using and they have returned the results of
5.425 MVA sc and 4.697 MVA sc.
RE: short circuit MVA rating
Rafiq Bulsara
http://www.srengineersct.com
RE: short circuit MVA rating
RE: short circuit MVA rating
But they have to tell you.
"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)
RE: short circuit MVA rating
RE: short circuit MVA rating
Rafiq Bulsara
http://www.srengineersct.com
RE: short circuit MVA rating
With all due respect, you need to get the understanding of the basic of short circuit calculations. I suggest you get a good book such as IEEE Red Book and familiarize your self with the basics or pay someone to help you out.
Even some google search on the topic will get you information that is useful, if you know enough to separate good info from the bad one.
Rafiq Bulsara
http://www.srengineersct.com
RE: short circuit MVA rating
As Rafiq said, you are going to need more help than what you will be able to get here.
Alan
RE: short circuit MVA rating
It would help if we knew what you plan to do with the short circuit data when you get it.
"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)